With wireless communication, there is demand to effectively utilize the wireless frequency bands used as the propagation channel. For this reason, methods that multiplex streams for communicating among multiple users in a frequency domain are widely used. NPL 1 describes a spectrum-overlapped resource management (SORM) scheme that allows partial overlapping (hereinafter referred to as overloading) of a frequency band used by multiple streams. Consequently, the SORM scheme has superior spectral efficiency over frequency-division multiplexing (FDM), which controls the frequency bands to be used in a complete exclusive manner.
However, with wireless communication, errors may occur in transmitted information due to thermal noise in the receiver and frequency-selective phasing, and the spectral efficiency may drop. In order to correct errors in information, the application of turbo coding and decoding has been proposed (see PTL 1 and NPL 1).
In turbo coding, two recursive systematic convolutional (RSC) coders having the same connection are used, and the information bits constituting a receive signal are input as-is into one of the coders. The information bits are permutated by an interleaver and input into the other coder. Thus, information bits convoluted with two independent constraint parameters are generated. The turbo decoder decodes the information bits using two maximum a posteriori probability (MAP) estimators. The transmit bits may be detected by exchanging reliability information regarding the information bits obtained by decoding. In this way, by applying two independent constraint parameters and repeating the process, the reliability of the information bits gradually improves, and the transmit bits are detected.